Never an integer? |
Consider the sequence defined by:
(2N+K)!
U[N] = Sum [ ------------------ ] K = 0,1,..,N
(2N-2K)!*(3K+1)!
It starts like this:
U[1] = 5/4
U[2] = 51/14
U[3] = 277/20,
U[4] = 1497/26
It seems that all elements are rationals.
Actually, some elements are integers.
What is the 1st N for which U[N] is an integer?
What is the value of U[N] modulo 10^50? (It's a BIG number)
Answer format: Index,Value
Hint:
Consider the sequence V[N] = (6N+2)*U[N] and show it satisfies a recurrence relation:
V[N+3] = A*V[N] + B*V[N+1] + C*V[N+2] (A,B,C integers)
Warning:
Finding the answer will be quite demanding for your machine ...
| All Submission |
Problem Maintainer : Philippe_57721
@sinan My timing is too embarassing to tell.
But some clever people managed to solve this problem in half a minute.
How long did it take you to get the answer for this quite demanding problem? I did some analysis but I cannot decide if I set out for this one.
This is a test
\begin{equation} \nonumber
\overline{m} =
\frac
{\displaystyle
\sum_{i=1}^{nind}p_i \times {V(k)}_i
}
{\displaystyle
\sum_{i=1}^{nind}p_i
}
\end{equation}
IE8 refuses now to show this page.
I had to use Firefox to type in this comment.